#include <bits/stdc++.h>
using namespace std;

int main() {
    ios_base::sync_with_stdio(false);cin.tie(nullptr);
    int T; cin >> T;
    while(T--){
        int N; cin >> N;
        vector<int> v;
        for (int i = 0; i < 2*N; ++i) {
            int t; cin >> t;
            v.emplace_back(t);
        }
        sort(v.begin(), v.end());
        cout << abs(v[N-1] - v[N]) << "\n";
    }
    return 0;
}